1. Field of the Invention
The present invention relates to an image processing apparatus, an imaging apparatus, and an image processing method, and in particular to an image processing apparatus, an imaging apparatus, and an image processing method for processing a fluorescence image based on fluorescence from an object.
2. Description of the Related Art
Conventionally, in the medical field, endoscope systems are used when an inside of an organ of a subject is observed. In such an endoscope system, typically, a flexible insertable unit in an elongated shape is inserted into a body cavity of a subject such as a patient, a living tissue in the body cavity is irradiated with white light by the flexible insertable unit thus inserted, and reflected light thereof is received by an imaging unit in the flexible insertable unit, thereby capturing a white-light image of the living tissue. Such a white-light image of the living tissue is displayed on a display unit of the endoscope system. A user such as a doctor observes the inside of the body cavity of the subject through the white-light image of the living tissue displayed on the display unit of the endoscope system.
By contrast, in the field of endoscopes in recent years, an endoscope system is developed in which a living tissue in a body cavity is irradiated with excitation light other than white light by a flexible insertable unit inserted into the body cavity, and autofluorescence or drug-induced fluorescence generated from the living tissue based on the irradiation of the excitation light is received by an imaging unit in the flexible insertable unit, thereby capturing a fluorescence image of the living tissue (e.g., Japanese Laid-open Patent Publication No, 2007-229053). Furthermore, another endoscope system is developed in which a drug-induced fluorescence image of a lesion is captured based on drug-induced fluorescence generated from the lesion serving as an object, and the brightness of the drug-induced fluorescence image thus captured is normalized, thereby correcting the intensity of the fluorescence attributed to differences in the distance from the object to the imaging unit (e.g., Japanese Laid-open Patent Publication No. 2008-183349). The image processing apparatus of the endoscope system disclosed in Japanese Laid-open Patent Publication No. 2008-183349 acquires a drug-induced fluorescence image and an autofluorescence image of a target region to be observed in the body cavity sequentially, generates a normalization image based on the autofluorescence image, and divides the brightness value of the drug-induced fluorescence image by the brightness value of the normalization image, thereby normalizing the brightness of the drug-induced fluorescence image.